A&P here with both aircraft and motorcycle experience.

There is a pretty significant difference in use for the average aircraft owner and motorcycle owner. The plane can and often does sit idle, outside or in a shadeport for some time. It is not uncommon for the plane to be idle for weeks after being flown. The engines are also built to much looser standards than even the old airheads were. That's because of the materials used and the expected expansion they get when they get warmed up. They are also built using 1940's through 1950's tech. Open breather tubes into the crankcase are a good example. They will have a simple breather tube that has no valve in it so air can and does move into the engine. If you are in a severe climate area like say Florida and the bird is stored outside, then you might want to insure that you do what you can to prevent corrosion.

On the other hand, aircraft engines rarely have bottom end problems. The rings and valves are more trouble prone. Aircraft oil already has a good percentage of additives, enough so that when breaking in an engine, either new or from overhaul, it is recommended that you use straight mineral oil made without wear additives for the first 25 to 50 hours of active engine operation, to help the rings seat. Once that is done then use regular oil. This helps prevent the cylinders from getting glazed where the rings never fully seal and the engine uses an excessive amount of oil.

In regards to motorcycle engines, even for those who store the bike, the additive may have some benefit. If you use the bike regularly in the riding season there is no need for the stuff. When you put the bike to bed for the winter, warm it up then change the oil and filter. Put the additive in and ride the bike a few miles well into normal temperatures (say 20 or so miles) then put it away. Don't forget the gas treatment unless you drain the tank and fuel system.

Frankly I wouldn't use anything like this stuff for normal motorcycle operation. If you drive it regularly, the insides are not going to lose the coating of oil and have a corrosion problem. "Pickling" the engine for storage it's not a bad idea and spending 12 bucks a year is not that expensive. Then again you could also do like the military did back in the recip days and pull the plugs, squirting a bit of oil into each cylinder then rotate the prop manually a few turns to spread it around then replace the plugs.